This invention relates to a method of carrying out conversion between a cyclic code sequence and a general code sequence. This invention relates also to an encoder and a decoder for carrying out the conversion.
In satellite communication of the known TDMA (time division multiple access) type, a cyclic code sequence is transmitted and received to improve the performance. It is therefore necessary to carry out conversion between a cyclic and a general code sequence, each consisting of a plurality of code blocks. More particularly, the general code sequence is encoded in a transmitter into the cyclic code by supplementing data bits of each code block of the general code sequence with a predetermined number of check bits that forms a cyclic code together with the data bits contained in that code block. The cyclic code sequence is decoded into the general code sequence in a receiver by removing the check bits of each code block.
Each cyclic or general code sequence as called herein has a variable duration determined by a burst that is known in the art. On the other hand, each code block is normally given a normal code block period. It is therefore necessary that each code sequence should comprise an additional code block of a variable additional code block period in addition to such normal code blocks. It is the practice to make the additional code block period shorter than the normal code block period.
A method of carrying out such a conversion is proposed in a Japanese technical paper, Densi Tusin Gakkai Tusin-hosiki Kenkyukai Siryo CS 77-66 (Papers for Communication System Study Committee of the Institute of Electronics and Communication System Engineers of Japan, No. 77-66), contributed by Keiichiro KOGA, Yutaka YASUDA, Takuro MURATANI, Yoshihiro IWADARE, and Katsuhiro NAKAMURA, under the title of "TDMA Hosiki ni taisuru Ayamari Teisei Hugo no Tekiyo (Application of FEC Coding to TDMA Systems)" and published in September, 1977. According to this paper, conversion between an additional code block of one of the cyclic and the general code sequences and a corresponding additional code block of the other of the sequences is carried out by preparing a dummy bit series for the data bits of the additional code block of the sequence that should be converted to the other sequence. However, the technical paper does not disclose how to discriminate the additional code block from the normal code blocks.